1. Field of the Invention
The present invention relates to a structure of a front body of an automobile, and more particularly to a structure of a suspension frame of a strut type suspension provided on the front body of the automobile.
2. Description of Related Art
In a case where a suspension provided on the front body of an automobile is a double wishbone type, proper changes in the toe angle of tires can be obtained even if a steering gear case is placed at a position higher than the cross member and the suspension frame of the body to which a steering gear case is attached. For example, also in a case where the steering gear case (a pinion case) 33 is attached through a mount bracket 31 and a fixture 32 to an upper face of a suspension frame 30 fixed to the body frame so that the steering gear case 33 is placed at a position higher than the suspension frame 30 as shown in FIG. 10, proper changes in the toe angle of the tires can be obtained.
On the other hand, if the suspension is a strut type, a position in which the steering gear case is placed should be set as low as possible and the length of a tie-rod should be increased with respect to a lower control arm in order to obtain proper changes in the toe angle of the tires. For this reason, in an automobile having a strut type suspension, the steering gear case 33 is attached to the rear face of the suspension frame 30 through a mount member 34, and the lower portion of the steering gear case 33 is provided below the suspension frame 30 as shown in FIG. 11.
However, if the steering gear case 33 is placed in a low position in a layout in which the steering gear case 33 is provided in front of the front wheels, there is a possibility that a disorder might be caused; for example, the steering gear case 33 might come in contact with a road surface while fairing bad road conditions. Therefore, an under guard 36 has conventionally been provided below the steering gear case 33 between the suspension frame 30 and the cross member 35 of the body frame in order to protect the steering gear case 33 as shown in FIG. 11.
FIG. 12 shows a position at which an A-shaped lower control arm 71 is attached to the front suspension. The lower control arm 71 connects the tire 72 (or wheel) and the frame 73. The frame 73 is attached to the main frame or the suspension frame which is not shown.
FIG. 13 shows the connection between the lower control arm 71 and the frame 73. As shown in FIG. 13, mount brackets 74 and 75 of the lower control arm 71 are fixed to the frame 73 by welding. The lower control arm 71 holds bush portions 71a and 71b between protruding pieces of the mount brackets 74 and 75 so that a bolt 76 and a nut 77 are tightened as shown in FIG. 14.
As shown in FIG. 13, the mount brackets 74 and 75 of the lower control arm 71 are welded to the frame 73 respectively as described above. By the influence of heat or the like, therefore, it is difficult to obtain an accurate dimension indicated at L1 between the mount brackets 74 and 75. Furthermore, a lower control arm 71 also has parts such as bushes fitted in the bush portions 71a and 71b by pressure so that a dimension indicated at L2 can be obtained accurately only with some difficulty.
For this reason, a clearance s is provided such that the bush portions 71a and 71b can easily be attached to the mount brackets 74 and 75 even if the dimensions are not precise when they are to be attached.
With the structure of the front body shown in FIGS. 10 and 11, the under cover 36 needs to be provided as a separate member in order to protect the steering gear case 33. Therefore, the number of parts and assembly efforts are increased, and the weight of the body increases. Furthermore, it is necessary to cause a steering pinion 37 (see FIGS. 10 and 11) to approach a portion of the inside of the body (a central side of the body) in order to set the tie-rod as long as possible. In this case, however, the joint angle of the connecting portion with the steering column increases so that steering force fluctuates more greatly, resulting in a poor sense of steering.
On the other hand, it may be considered to move a steering rack shaft (not shown) upward so that the steering gear case 33 is placed at a higher position in order to protect the steering gear case 33. In this case, the length of the tie-rod needs to be increased in order to properly change the toe angle. Correspondingly, the length of the steering rack shaft is relatively decreased. Consequently, the required steering turn angle cannot be obtained.
With the structure of the front body shown in FIGS. 13 and 14, when the mount brackets 74 and 75 and the bush portions 71a and 71b are fastened with the bolt 76, the mount brackets 74 and 75 should also be fastened to close clearance s. Therefore, the mount brackets 74 and 75 are deformed and large tightening torques are required. Furthermore, even after the lower control arm is mounted, the bolt 76 and the nut 77 may become loose, and the internal stress of the mount brackets 74 and 75 may disadvantageously occur.
As shown in FIG. 15, furthermore, dimensional errors between a mounting point a of a ball joint of the lower control arm and a point b of the rack and pinion of the steering also increase so that the accuracy of alignment is reduced.